FIG. 6 is a schematic view of conventional arc welding apparatus 501 disclosed in PTL 1. In arc welding apparatus 501, wire feeder 900 feeds welding wire 901 with torch cable 902 and feeds welding wire 903 with torch cable 904, thereby feeding the wires to welding torch 910. Welding torch 910 has inlet passage 911 to which torch cable 902 is connected, inlet passage 912 to which torch cable 904 is connected, and outlet passage 913. Inlet passage 911 and inlet passage 912 merge together at joint 914. Joint 914 is connected to outlet passage 913. Wire feeder 900 causes welding wire 901 to protrude from nozzle opening 915 provided at a tip of welding torch 910 by feeding welding wire 901 to welding torch 910 and causing welding wire 903 to stand by within torch cable 904.
FIG. 7 is a schematic view of conventional wire feeding system 502 disclosed in PTL 2. In wire feeding system 502, wire feeder 920A rotates wire reel 922A about spool shaft 921A to feed wire 923A, and wire feeder 920B rotates wire reel 922B about spool shaft 921B to feed wire 923B. Wire 923A passes through conduit tube 940A, feed guide opening 950A, branch line 950, feed guide opening 950C, and conduit tube 940, and is fed to welding torch 930. Wire 923B passes through conduit tube 940B, feed guide opening 950B, branch line 950, feed guide opening 950C, and conduit tube 940, and is fed to welding torch 930. Wire 923A and wire 923B are switched based on the presence of wire 923A which is detected by wire detecting device 941A, and the presence of wire 923B which is detected by wire detecting device 941B.